Researchers at HP Labs, UC Santa Cruz and 3M have jointly developed a novel printing method that mimics the light interactions that real objects undergo. The technique, which uses specially designed "reflectance paper" covered with thousands of tiny dimples, was presented recently at Siggraph 2012.

Real objects vary their appearance as they are illuminated from different directions, and our brains are very good at inferring 3D shape from these sorts of lighting interactions. Photographs capture those interactions from a single, static lighting environment but our reflectance paper can display appearance from arbitrary lighting directions.

Photographs of the same prototype reflectance print being

illuminated from 2 different directions.

For example, imagine a print of a statue on reflectance paper. The statue could be made to cast shadows to the right when the print is viewed with lighting from the left and to cast shadows to the left when the print is viewed under lighting from the right. In fact, all lighting interplay can be captured, not just shadows. That includes diffuse and specular reflectance, subsurface scattering, interreflections, anything physics can throw at us.

The mathematical "reflectance function" describes how light is reflected from each point on an object as a function of incoming lighting direction. Measuring the reflectance functions for an object or scene can be done by taking photographs lit from many different lighting directions.

Opaque ink on a transparency selectively blocks specified lighting

directions from being seen by the user.

Our new printing technique allows the paper to embed an arbitrary reflectance function for every pixel, allowing its appearance to change arbitrarily with lighting angle. It works by starting with a specially-designed substrate covered with shiny, reflective dimples. By printing on a transparency sheet above the dimples, specific lighting directions can be blocked selectively from the user, allowing an arbitrary reflectance function to be represented.

My HP Labs co-author Ramin Samadani noted that “currently the quality of our prints is nowhere near what could be described as photorealistic, but we believe that it is a matter of engineering and nothing fundamental stands in the way.” Museum curators, historians and forensics specialists already use computational techniques my colleagues and I have developed at HP Labs to see more detail on the surface of the objects. Our most recent development would now allow them to produce hard copies too.